Electronic switching circuit arrangements

ABSTRACT

An electronic, high-voltage switching arrangement for switching the final anode voltage of a beam-penetration type color C.R. tube. The arrangement comprises separate color-enable-signal voltage coding transistors, an I.C. transistor drive amplifier and a thermionic electron tube cathode-follower providing feedback from a tapped cathode potentiometer.

ilited tatea atea Humphrey s 1451 May 22, 1973 References Cited UNITED STATES PATENTS 7/1967 Guillette ..l78/5.4 W X 6/1965 Von Kummer.. ..328/213 X 3/1961 Crowther 328/213 5/1969 Ting ..315/30 /1971 Bacon ..315/27 TD 5/1970 Smith ..l78/5.4 R

Primary Examiner-Carl D. Quarforth Assistant Examiner-E. E. Lehmann AttorneyStevens, Davis, Miller & Mosher 315/27 TD; 328/213, 209; 313/42 R, 92 P, 17, 31; 178/5.4, 5.4 w, 5.4 PE

ABSTRACT An electronic, high-voltage switching arrangement for switching the final anode voltage of a beam-penetration type color C.R. tube. The arrangement comprises separate color-enable-signal voltage coding transistors, an LC. transistor drive amplifier and a thermionic electron tube cathode-follower providing feedback from a tapped cathode potentiometer.

6 Claims, 3 Drawing Figures +24V i +5VREFERENCE U ENABLE ORANGE MAE MAE 29 ENABLE GREEN. 1 70 i M ,76 7 H 7 721: f 51 46 4/ 33 i 32 22 26 60,

; -2 imp 52 47, f f 12 55 56): 23 %59 74 4 .54 l E w I 36 -1 4Q l 44 1 T l 1 i 1 l? 1 39 7 I 55 A 1 1 158 r 1 A5 ml 1 l 4 4 5. L '24vl f aw A a n EEE EAEN L/NEW Patented May 22, 1973 3 Sheets-Shoat 5 QZEM NW ELECTRONIC SWITCHING CIRCUIT ARRANGEMENTS This invention relates to electronic switching circuit arrangements and, in particular, to high voltage switching circuit arrangements for controlling color cathode ray display tubes.

Cathode ray tubes are known for providing a display in a plurality of color in which the control of display color is effected by control of the EHT voltages to the final anode of the tube.

The switching arrangement used is required also to provide the focus anode of the tube with a voltage proportional to that of the final anode. Previously, switching of the EHT voltages has been effected by a circuit arrangement comprising a cathode follower and electron tube drive stages.

It has been found that such switching circuit arrangements have disadvantages in that the operating speed of the circuit is too slow, the power supply required by such valve circuits is high and the combination of such circuits with present day digital logic circuits is incon venient.

The object of the present invention is to provide an improved electronic switching circuit arrangement having regard to the aforementioned difficulties.

Accordingly, the present invention provides an electronic switching circuit arrangement, for switching the final anode voltage of a color display cathode ray tube comprising a transistor drive amplifier and an output stage including a thermionic valve operating as a cathode follower, the drive amplifier having a plurality of input terminals, one terminal for the enable signal of each display color of the tube, each input terminal being connected to the input circuit of a transistor, each said transistor having its output circuit connected to the input of a further amplifier and feedback being provided from the output of the said cathode follower to the input of said further amplifier.

In order that the invention may be more fully understood and readily carried into practice, one embodiment thereof will now be described in detail, by way of example, with reference to the accompanying drawings, of which:

FIG. I is a schematic circuit diagram of the color input signal control and LC. amplifier part of an EHT switching circuit arrangement;

FIG. 2 is a schematic circuit diagram of the associated cathode follower output part of the circuit arrangement for supplying the switched final anode and focus anode potentials for a color display cathode ray tube; and

FIG. 3 is a schematic circuit diagram of LC. amplifier l of FIG. 1.

Referring now to the drawings, the particular embodiment there shown comprises an LC. amplifier 1 (FIG. I) which controls, by way of an intermediate electron tube 2 (FIG. 2) a electron tube 3 which is connected as a cathode follower between a +2lKV high voltage line 4 and a zero voltage line 5. The output voltage at the cathode of electron tube 3 is sampled by a potential divider, comprising serially connected resistors 6 to 10, and the sampled voltage is made available at terminal 12 (FIG. I) by way of feedback line 11 connected to the junction of resistors 9 and 10. The feedback voltage at terminal 12 appears across serially connected resistors 13, 14 and 15 and this voltage is selectively attenuated by a potential divider comprising resistor l6 and three alternatively switched resistor networks selectively controlled by Enable Orange, Enable Yellow and Enable Green control signals at terminals 17, 18 and 19, respectively, in a manner later described. The selectively attenuated voltage is applied, through series resistor 20, to input terminal 22 of LC. amplifier 1. Most of the gain of the loop described is provided by amplifier 1, the output terminal 26 of which controls the cathode potential of electron tube 2, by way of terminal 60 (FIG. 1) and terminal 60 (FIG. 2).

Considering the circuit arrangement shown in greater detail, a +24V line from terminal 28 is connected through series resistor 29 to terminal 27 of amplifier 1. A diode 30 is connected between amplifier terminals 27 and 22. A +5V reference voltage line from terminal 31 is connected through series resistor 32 to terminal 23 of amplifier 1. A diode 33 is connected between amplifier input resistors 20 and 32. A 24V line from terminal 34 is connected through series resistor 35 to terminal 24 of amplifier 1. A diode 36 is connected between amplifier terminals 22 and 24 and a diode 37 is connected between amplifier terminal 24 and zero voltage line 5. A diode 38 is connected between amplifier terminal 27 and zero voltage line 5.

Each color enable signal, at terminal l7, l8 and 19, controls a transistor which switches, into serial circuit with resistor 16, a serial combination of a fixed and a variable resistor. Thus, terminal 17 is connected through resistor 39 to the base electrode of a transistor 40. Transistor 40 has fixed resistor 41 and variable resistor 42 serially connected from resistor 16 to its collector electrode. Its emitter electrode is connected to zero voltage line 5. A diode 43 is connected from its base electrode also to zero voltage line 5. Similarly, terminal 18 is connected through resistor 44 to the base electrode of a transistor 45, the output circuit of which transistor includes resistors 46 and 47. A diode 48 is connected from the base electrode of transistor to the zero voltage line 5. Similarly, terminal 19 is connected through resistor 49 to the base electrode of a transistor 50, the output circuit of which transistor includes resistors 51 and 52. A diode 53 is connected from the base electrode of transistor to the zero voltage line 5.

Resistors 42, 47 and 52 are pre-set variable resistors and respectively provide set orange, set yellow and set green control.

A terminal 54 is connected to the junction of resistors l4 and 15. Preset variable resistor 14 provides a set red control.

Shunt capacitors 55, 56, 57 and 58 are, respectively, connected between terminal 54, amplifier terminal 23, amplifier terminal 27, amplifier terminal 24 and zero voltage line 5.

Amplifier terminal 26 is connected to terminal 60 (FIG. 1) which is connected to terminal 60 (FIG. 2). Terminals 5 and 11 (FIG. 1) are similarly connected to the correspondingly referenced terminals in FIG. 2.

Referring, now, particularly to FIG. 2, terminal 60 is connected to the cathode of electron tube 2 and through a resistor 61 to the zero voltage line 5. The grid of tube 2 is tied to the zero voltage line 5 through a resistor 62. The anode of valve 2 is connected to the +21KV EHT line at terminal 4 through resistor 63 and is directly connected to the grid of tube 3.

The heater of tube 2 is supplied from terminal pair 64 and the heater of tube 3 is supplied from terminal pair 65.

The cathode of tube 3 is connected to the zero voltage line 5 by way of serially-connected resistors 6, 7, 8, 9 and 10, of which resistor 8 is a preset potentiometer. The anode of tube 3 is connected directly to the +21KV EHT line at terminal 4. A diode 66 is connected from the electron tube grid to the junction of resistors 6 and 7, which junction is connected to EHT switch output terminal 67. Resistor 6 is shunted by capacitor 69. The slider of potentiometer 8 is connected to focus potential terminal 68.

Referring now to FIG. 3, the schematic circuit diagram there shown is the circuit of amplifier 1 of FIG. 1. This is a commercially available multi-stage operational amplifier of a type constructed on a single silicon chip and marketed by Marconi-Elliott Microelectronics Limited under their type number 7741C.

The terminal numbering shown in FlG.3 corresponds to that shown in FlG.l and further corresponds to the manufacturers pin numbering, with an additional we fix The maximum permitted supply voltage between terminal 27 and terminal 24 is 18 volts, permitting a differential input voltage between terminals 22, 23 and terminal 24 of 30 volts.

Externally of the amplifier unit of FIG.3 an offset adjustment resistor 59 is connected between terminals 21 and 25, as shown in FIG. 1. Also, a feedback resistor 70 is connected between terminals 26 and 22.

Referring now to FlGS. l and 2, the color cathode ray tube whose EHT voltage is controlled at terminal 67 provides four display colors at different EHT volt age values as follows:

RED 6.0 KV ORANGE 8.0 KV YELLOW 9.8 KV GREEN l2.5 KV

Terminal 54 is a voltage monitor point at which there are provided attenuated voltages corresponding to those appearing at terminal 67.

Considering now the manner of operation of the circuit arrangement of FIGS. 1 and 2, it is to be noted that digital enable" voltage inputs are selectively provided at terminals l7, l8 and 19 from standard 5 volt transistor-transistor logic-circuits, not shown in the drawings. Such circuits provide typically an enable or 1 level of +3.5 volts and a disable or 0 level of zero volts.

When the circuit arrangement of FIGS. 1 and 2 is put into operation, with no enable voltage on any of terminals 17, 18 and 19, the output at terminals 67 is 6.0 KV, which corresponds to RED display color of the associated tube.

The colors available need not be selected in the stated sequence corresponding to increasing, or decreasing, EHT voltages but this sequence of color selection provides minimum switching times. To select GREEN, in place of RED, for example, terminal 19 is set to l, by application of the enable voltage of +3.5 volts, as stated earlier. Transistor 50 is turned on", by way of resistor 49. Thereby, resistors 51 and 52 are connected into circuit, reducing the potential of line 71 and the potential of terminal 22 of amplifier 1. Terminal 22 is the inverting input of amplifier 1, see

FIG. 3, and the output at terminal 26 is caused to go positive.

The gain of amplifier l is limited to 1,000 times, by resistors 20 and 70.

The output voltage at terminal 26 drives the cathode of electron tube 2 by way of terminal 60. Tube 2 is connected to provide non-inverting voltage gain. Thus, the anode of tube 2, and the grid of valve 3, will be driven positive. Diode 66 will not conduct. Thus, tube 3 will provide a low impedance output drive when the output is positive-going.

Circuit operation to select colors ORANGE and YELLOW is similar to that described to select GREEN. An enable" pulse l is applied to terminal 17 and 18, respectively. Transistor 40 or 45, respectively, is turned on by way of resistor 39, 44, respectively, to connect into circuit resistors 41, 42 or resistors 46, 47, respectively. The potential at amplifier input terminal 22 is set correspondingly.

Negative feedback is at all times provided, according to the amplifier output at terminal 26, and corresponding potential at the junction of resistors 9,10, by way of feedback line 11, to terminal 12. The effect of the feedback is to restore the potential on line 71 to the potential of the +5V reference value at terminal 31.

The color RED is selected in the absence of any other selected color, that is when no enable pulses are applied to any of terminals l7, l8 and 19. In this condition, all transistors 40, 45 and 50 are turned off. The input to terminal 22 of amplifier 1 is thereby increased. The cathode, and hence the anode, of tube 2 is driven negative. Diode 66 is caused to conduct and tube 3 is turned off. Tube 2 thus provides the low impedance output drive when the output is negative-going.

Rapid switching times are obtained with the specific embodiment of the circuit arrangement described. With a total load capacitance comprising the tube 3 heater transformer of approximately 30pF and cathode ray tube capacitance of approximately 330pF., the output (terminal 67) waveform rise times are as follows:

I60 microsecs. 250 microsecs. 850 microsecs. 450 microsecs.

It is to be noted that a number of important impractical advantages are obtained with the embodiment of the invention particularly described. The circuit arrangement provides a complete interface between standard transistor to transistor logic control circuiting and the high-voltage input terminals of the multi-color display tube. The color change switching times are minimal, providing only brief interruption of data displayed. An unregulated, and therefore inexpensive, form of 2llKV power supply only is required, because the switched output voltages are set by the negative feedback loop and are thus independent of supply variations.

1 claim:

1. An electronic switching circuit arrangement, for switching the final anode voltage of a color display cathode ray tube comprising a transistor drive amplifier and an output stage including a thermionic electron tube operating as a cathode follower, the drive amplifier having a plurality of input terminals, one terminal for the enable signal of each display color of the tube, each input terminal being connected to the input circuit of a transistor, each said transistor having its output circuit connected to the input of a further amplifier and negative feedback being provided from the output of the said cathode follower to the input of said further amplifier.

2. An electronic switching circuit arrangement as claimed in claim 1, including tapped potentiometer means, connected in the cathode circuit of said cathode follower, for providing focus anode potentials for said color display cathode ray tube.

3. An electronic switching circuit arrangement as claimed in claim 2, in which said color display cathode ray tube provides a display in a sequence of a plurality of different colors corresponding to increasing final anode voltages, including means for selecting enable signals in the same order as said sequence, for switching to an increased final anode voltage, and in the reverse order as said sequence, for switching to a decreased final anode voltage.

4. An electronic switching circuit arrangement as claimed in claim 3, in which said negative feedback is provided from the said tapped potentiometer means connected in the cathode circuit of said cathode follower.

5. An electronic switching circuit arrangement as claimed in claim 4, in which the cathode circuit of said cathode follower includes a potentiometer including a first resistor connected to the grid of said cathode follower by way of a diode, a second resistor having a preset tap, for providing said focus anode potentials, and a third resistor providing said feedback voltage.

6. An electronic switching circuit arrangement as claimed in claim 5, in which the said drive amplifier is a multi-stage operational amplifier including a feedback circuit. 

1. An electronic switching circuit arrangement, for switching the final anode voltage of a color display cathode ray tube comprising a transistor drive amplifier and an output stage including a thermionic electron tube operating as a cathode follower, the drive amplifier having a plurality of input terminals, one terminal for the enable signal of each display color of the tube, each input terminal being connected to the input circuit of a transistor, each said transistor having its output circuit connected to the input of a further amplifier and negative feedback being provided from the output of the said cathode follower to the input of said further amplifier.
 2. An electronic switching circuit arrangement as claimed in claim 1, including tapped potentiometer means, connected in the cathode circuit of said cathode follower, for providing focus anode potentials for said color display cathode ray tube.
 3. An electronic switching circuit arrangement as claimed in claim 2, in which said color display cathode ray tube provides a display in a sequence of a plurality of different colors corresponding to increasing final anode voltages, including means for selecting enable signals in the same order as said sequence, for switching to an increased final anode voltage, and in the reverse order as said sequence, for switching to a decreased final anode voltage.
 4. An electronic switching circuit arrangement as claimed in claim 3, in which said negative feedback is provided from the said tapped potentiometer means connected in the cathode circuit of said cathode follower.
 5. An electronic switching circuit arrangement as claimed in claim 4, in which the cathode circuit of said cathode follower includes a potentiometer including a first resistor connected to the grid of said cathode follower by way of a diode, a second rEsistor having a preset tap, for providing said focus anode potentials, and a third resistor providing said feedback voltage.
 6. An electronic switching circuit arrangement as claimed in claim 5, in which the said drive amplifier is a multi-stage operational amplifier including a feedback circuit. 